n = input()
if len(n) == 4:
  n1 = n[0]
  n2 = n[1]
  n3 = n[2]
  n4 = n[3]
  sp = [int(n1), int(n2), int(n3), int(n4), int(n1+n2), int(n1+n2+n3+n4), int(n2+n3), int(n2+n3+n4), int(n3+n4)]
  sp.sort(reverse = 1)

  for x in sp:
    F = 1
    for d in range(2, x//2+1):
      if x % d == 0:
        F = 0 
        break
    if F == 1:
      print(x)
      break
  if F==0:
      print('0')
else:print('0')
